a ring around your wings
Tests have shown that there are in fact less vibrations within a contained blade. The blades feather just as per normal as they are allowed to pivot within the ring. Track and balance needs to be perfect as does any rotor system. Aerodynamics show positive results when evaluated by FDA. Increased drag is compensated for by increased eficiency around blade tips Due to improved tip loss factor. Stuff more weight on the tips of Robinson blades, and they will depart from the hub unless the hub if beefed up. Heavier hub, more power required to lift. Bug.